Tomato is a well known source of vitamins, minerals and antioxidants, which make up the essential components of a balanced healthy diet. It is also widely accepted that quality attributes such as colour, flavour and firm texture strongly influence consumer choice in the purchase of this expensive and readily perishable crop.
Harvesting tomato fruit when ripening has set in would make maturity determination easier as it would be based on visible peel color and would assure full quality development. After harvest, ripening continues and softening advances, increasing the susceptibility of the fruit to handling damage and limiting the marketing period. Slowing down the ripening and softening stages would allow harvesting, transport and storage of partially ripe but firm fruit (T. Chanthasombath et al, 2008).
Ripening mutants in tomato such as Colourless non-ripening and ripening inhibitor have yielded important insights into an emerging genetic framework which regulates ripening and modulates fruit firmness (Thompson et al, 1999; Vrebalov et al, 2002; Eriksson et al, 2004; Manning et al, 2006). Delaying ripening and softening may be achieved by employing modified atmosphere packaging (MAP) which has been extensively studied as a simple and cheap method of prolonging shelf life of many fruits and vegetables including tomato (Batu & Thompson, 1998, Exama et al, 1993, Geeson et al, 1985), however it increases the cost of packaging and handling of fruits. Existing methods to enhance fruit firmness in conventional plant breeding programs rely on screening fruit firmness differences in fruit harvested from mature plants. Any identification of enhanced fruit firmness in this scenario will largely be down to chance. Currently it is not financially viable or efficient to breed for enhanced fruit firmness due to the cost and complexity of growing and phenotyping large numbers of plants.
To bridge the gap between the emerging model for the regulation of fruit ripening and a full knowledge of the components involved in controlling fruit firmness will require additional strategies to those based on either targeting genes for known cell wall-related proteins or investigating pleiotropic ripening mutants. Fruit firmness is a quantitative trait involving many genes and yet the identity of the majority of these genes remains elusive.
Wild tomato species offer a rich and largely unexplored source of new genetic variation for breeders. Tanksley and Zamir (Frary et al, 2000; Fridman et al, 2004) have demonstrated that this source of genetic diversity can be used to understand the molecular basis of important fruit quality traits and provide new material for breeding.
The need clearly exists for the efficient and early selection of genotypes that are likely to display firmer fruit when mature. However, previous work in the texture area has been hampered by problems of reproducibility and precision.